LicenseExpressionFAQ

Why was the License Terms Expression Language introduced in the SPDX 2.0 Specification

The SPDX 1.x Specification and earlier versions of the License List had a limited ability to represent more complex license situations typically found in practice. Examples of such complexity can be found at: http://wiki.spdx.org/view/FileNoticeExamples . Additionally, earlier versions of the SPDX License List required the addition of multiple yet similar license identifiers in order to capture combinations of versions, the “or later” license genre (i.e. GPL-2.0 and GPL-2.0+) and the most common exceptions (e.g., GPL-2.0+-with-autoconf-exception or GPL-3.0-with-autoconf-exception). The SPDX Legal working group identified more than 30 additional distinct exceptions. If one tried to accommodate the many different permutations of the different exceptions with the “or later” cases, the license list would become bloated and unwieldy. For additional historical background information you can reference: http://wiki.spdx.org/view/Legal_Team/License_Expression_Review_1. All in all, the introduction of the WITH and ‘+” operators, and the additional of the new license list exceptions section, we are able to represent more sets of license terms found in practice while simultaneously streamlining the SPDX License List.

Why do we need a License Expression Language when projects are available under a single license?

Typically an open source project will start out making their software available under a single open source license but as some projects evolve they may leverage code from other successful projects governed by different licenses. Consequentially many successful projects end up with a diverse collection of files that are available under different licenses. Often programs are built from a diverse collection of files that are available under a composite set of different license terms. The SPDX License Expression language provides a way for one to construct license expressions that more accurately represent the licensing terms are typically found in open source software source code. Also some projects may offer their software under a multi-license choice where a license expression provides a formal way to representing this.